Some automotive fuels may exhibit rapid evaporation in response to diurnal variations in ambient temperature. Emissions resulting from such vapors may be reduced in automotive applications via evaporative emission control systems (EVAP), The EVAP systems include a fuel vapor storage canister containing adsorbent, such as carbon, that traps those fuel vapors and feeds them back to the vehicle's engine for combustion during canister purging operations, thus, reducing evaporative emissions from the vehicle and improving fuel economy.
In a canister purge operation, a canister purge valve (CPV) coupled between the engine intake and the fuel canister may be duty cycled, allowing for intake manifold vacuum to be applied to the fuel canister. On a boosted engine, that vacuum draw may be supplied via an ejector during boosted operation. Simultaneously, a canister vent valve coupled between the fuel canister and atmosphere can be opened, allowing for fresh air to enter the canister. Further, in some examples, a fuel tank isolation valve coupled between the fuel tank and the fuel canister may be closed to reduce the flow of fuel vapors from the fuel tank to the engine. This configuration facilitates desorption of stored fuel vapors from the adsorbent material in the canister, regenerating the adsorbent material for further fuel vapor adsorption.
Canister purge valves in EVAP systems that are duty cycled may have durability issues. Furthermore, opening and closing the CPV when there is a high pressure difference across the valve may result in the CPV experiencing higher loads and stresses as compared to situations where there is a lower pressure difference across the valve. Depending on the frequency and duty cycle of the purge valve opening and closing during pulsed flow control compared to engine firing frequency, more or less openings can occur at varying pressure differences, thus leading to unequal degradation of the valve due to the higher loads and stresses.
The inventors herein have recognized the above-mentioned issues and desires, and have developed systems and methods to at least partially address them. In one example, a method comprises purging a fuel vapor canister that captures and stores fuel vapors from a fuel system of a vehicle by synchronizing a timing of opening and closing events of a canister purge valve to correspond with instances where a pressure difference across the canister purge valve is lower as compared to higher in terms of pressure oscillations across the canister purge valve during purging the fuel vapor canister. In this way, issues related to durability of the CPV may be reduced or avoided.
In one example of the method, the method may further comprise adjusting the timing of the opening and the closing events of the canister purge valve in response to changes in the pressure oscillations across the canister purge valve during purging the fuel vapor canister.
As another example of the method, the method may further comprise controlling a duty cycle of the canister purge valve while synchronizing the timing of the opening and the closing events of the canister purge valve to correspond with the instances where the pressure difference across the canister purge valve is lower as compared to higher in terms of the pressure oscillations.
As another example, the pressure oscillations are a function of at least operating conditions of an engine that receives purge gasses from the fuel vapor canister. In such an example, the method may include determining a frequency, a phase, and an amplitude of the pressure oscillations across the canister purge valve in order to synchronize the timing of the opening and the closing events of the canister purge valve to correspond with the instances where the pressure difference across the canister purge valve are lower as compared to higher in terms of the pressure oscillations. In such a method, determining the frequency, the phase and the amplitude of the pressure oscillations may include mapping the pressure oscillations based on one or more of at least an engine speed, an engine load, a timing of opening and/or closing of intake and/or exhaust valves of the engine, and an ambient temperature. In another example, determining the frequency, the phase and the amplitude of the pressure oscillations may be based at least in part on feedback from a pressure sensor at the canister purge valve. In yet another example, determining the frequency, the phase, and the amplitude of the pressure oscillations may be based at least in part on a difference between an engine intake pressure and a fuel system pressure with the fuel system coupled to atmosphere, corrected for an offset that may be modelled as a function of a restriction of a buffer section of the fuel vapor canister.
In another example of the method, synchronizing the timing of the opening and the closing events of the canister purge valve to correspond with the instances where the pressure difference across the canister purge valve is lower as compared to higher in terms of the pressure oscillations across the canister purge valve may further comprise controlling a pulse width modulation signal to the canister purge valve based on the pressure oscillations across the canister purge valve.
In still another example of the method, synchronizing the timing of the opening and the closing events of the canister purge valve to correspond with the instances where the pressure difference across the canister purge valve is lower as compared to higher in terms of the pressure oscillations across the canister purge valve improves durability and reduces issues related to noise, vibration and harshness of the canister purge valve.
In yet another example of the method, synchronizing the timing of the opening and the closing events of the canister purge valve to correspond with the instances where the pressure difference across the canister purge valve is lower as compared to higher in terms of the pressure oscillations across the canister purge valve further comprises controlling the canister purge valve to open and/or close within a threshold time duration in relation to the pressure oscillations across the canister purge valve, the threshold time duration corresponding to when the pressure difference is lower as compared to higher in terms of the pressure oscillations across the canister purge valve.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.